Contraction-induced injury to single permeabilized muscle fibers from normal and congenitally-clefted goat palates.

Objective: Levator veli palatini muscles from normal palates of adult humans and goats are predominantly slow oxidative (type 1) fibers. However, 85% of levator veli palatini fibers from cleft palates of adult goats are physiologically fast (type 2). This fiber composition difference between cleft and normal palates may have implications in palatal function. For limb muscles, type 2 muscle fibers are more susceptible to lengthening contraction-induced injury than are type 1 fibers. We tested the hypothesis that, compared with single permeabilized levator veli palatini muscle fibers from normal palates of adult goats, those from cleft palates are more susceptible to lengthening contraction-induced injury.

Interventions: Congenital cleft palates were the result of chemically-induced decreased movement of the fetal head and tongue causing obstruction of palatal closure. Each muscle fiber was maximally activated and lengthened.

Outcome Measures: Fiber type was determined by contractile properties and gel electrophoresis. Susceptibility to injury was assessed by measuring the decrease in maximum force following the lengthening contraction, expressed as a percentage of the initial force.

Results: Compared with fibers from normal palates that were all type 1 and had force deficits of 23 +/- 1%, fibers from cleft palates were all type 2 and sustained twofold greater deficits, 40 +/- 1% (p = .001).

Conclusion: Levator veli palatini muscles from cleft palates of goats contain predominantly type 2 fibers that are highly susceptible to lengthening contraction-induced injury. This finding may have implications regarding palatal function and the incidence of velopharyngeal incompetence.